dpdb/code/main/java/com/example/dxsdpdb/MissionFragment.java

package com.example.dxsdpdb;

import android.os.Bundle;
import android.util.DisplayMetrics;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.HorizontalScrollView;
import android.widget.RadioButton;
import android.widget.RadioGroup;

import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.viewpager.widget.ViewPager;

public class MissionFragment extends Fragment implements ViewPager.OnPageChangeListener {

    private View view=null; // 碎片的布局实例
    private ViewPager viewPager; //内导航的碎片的容器
    private RadioGroup rgChannel=null; // 内导航由单选按钮组构成
    private HorizontalScrollView hvChannel=null; //单选按钮组可滚动动
    private String[] channelList = {"全部任务","待付款","待接受","待完成","已完成","已过期"}; //默认的内导航栏目
    private MissionFragmentAdapter adapter; //viewPager 的适配器

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
    }

    public MissionFragment() {
        // Required empty public constructor
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        // Inflate the layout for this fragment
        if(view==null){
            view=inflater.inflate(R.layout.fragment_mission, container, false);
            viewPager=(ViewPager)view.findViewById(R.id.vpNewsList);
            initViewPager(); //设置 ViewPager
            rgChannel=(RadioGroup)view.findViewById(R.id.rgChannel);
            hvChannel=(HorizontalScrollView)view.findViewById(R.id.hvChannel);
            initTab(inflater); //初始化内导航标签
            rgChannel.setOnCheckedChangeListener( //单选按钮的监听事件响应
                    new RadioGroup.OnCheckedChangeListener() {
                        @Override
                        public void onCheckedChanged(RadioGroup group,int checkedId) {
                            //单击某个选项按钮时 viewPager 进行切换
                            viewPager.setCurrentItem(checkedId);
                        }
                    });
        }
        return view;
    }

    private void initTab(LayoutInflater inflater){
        for(int i=0;i<channelList.length;i++){//以下添加单选按钮的实例到内导航
            RadioButton rb=(RadioButton)inflater.inflate(R.layout.tab_rb, null);
            rb.setId(i);
            rb.setText(channelList[i]);
            RadioGroup.LayoutParams params=new
                    RadioGroup.LayoutParams(RadioGroup.LayoutParams.WRAP_CONTENT,
                    RadioGroup.LayoutParams.WRAP_CONTENT);
            rgChannel.addView(rb,params);
        }
        rgChannel.check(0); //第一个选项
    }

    //设置 ViewPager 容器的适配器。

    private void initViewPager(){
        FragmentManager fragmentManager = super.getActivity().getSupportFragmentManager();
        //参数 channelList 将被适配器用来在动态切换碎片的时候实时创建碎片
        adapter=new MissionFragmentAdapter(fragmentManager, channelList);
        //设置 ViewPager 的适配器
        viewPager.setAdapter(adapter);
        viewPager.setOffscreenPageLimit(2);
        //设置显示第 1 个碎片
        viewPager.setCurrentItem(0);
        //设置 ViewPager 的切换监听
        viewPager.addOnPageChangeListener(this);
    }

    //以下三个方法是 ViewPager 的切换监听器 ViewPager.OnPageChangeListener 的事件处理方法
    //ViewPager.OnPageChangeListener 的实现采用了接口的方式
    @Override
    public void onPageScrolled(int i, float v, int i1) {
    }
    @Override
    //某个碎片被选中时的动作，对应的内导航标签将要滑动到屏幕中央，并且有下划线显示
    public void onPageSelected(int i) {
        setTab(i);
    }
    @Override
    public void onPageScrollStateChanged(int i) {
    }

    private void setTab(int idx){
        RadioButton rb=(RadioButton)rgChannel.getChildAt(idx);
        rb.setChecked(true);
        int left=rb.getLeft();
        int width=rb.getMeasuredWidth();
        DisplayMetrics metrics=new DisplayMetrics();
        super.getActivity().getWindowManager().getDefaultDisplay().getMetrics(metrics);
        int screenWidth=metrics.widthPixels;
        int len=left+width/2-screenWidth/2;
        hvChannel.smoothScrollTo(len, 0);
    }

}